Impact of the New Measurement of the ¹²C + ¹²C Fusion Cross Section on the Final Compactness of Massive Stars

Abstract

We discuss how the new measurement of the 12C + 12C fusion cross section carried out with the Trojan Horse Method affects the compactness of a star, i.e., basically the binding energy of the inner mantle, at the onset of the core collapse. In particular, we find that this new cross section significantly changes the dependence of the compactness on the initial mass with respect to previous findings obtained in Chieffi & Limongi by adopting the classical cross section provided by Caughlan & Fowler. A non-monotonic but well-defined behavior is also confirmed in this case and no scatter of the compactness around the main trend is found. Such an occurrence could impact the possible explodability of the stars.

Compact Binary Coalescences: Astrophysical Processes and Lessons Learned

“…Limongi and Chieffi [169] showed that there is a tight monotonic correlation between ξ 2.5 and m CO , which can be expressed as ξ 2.5 = 0.55 − 1.1m −1 CO , with m CO given in units of M [170]. This is in qualitative agreement with the simplified approach of Fryer et al [26], but different assumptions on carbon nuclear reaction rates might significantly affect the correlation (e.g., [171]).…”

A new 12C + 12C nuclear reaction rate: Impact on stellar evolution

“…Using solely the Hin reaction rates halves the lifetimes in comparison to the other models, due to the higher central temperature regime. Interestingly Chieffi et al (2021), using rates that are much higher than those of Caughlan & Fowler (1988) in the 0.1−1 GK range, find that C-burning occurs at lower densities (see Fig. 3 in Chieffi et al 2021).…”

“…Interestingly Chieffi et al (2021), using rates that are much higher than those of Caughlan & Fowler (1988) in the 0.1−1 GK range, find that C-burning occurs at lower densities (see Fig. 3 in Chieffi et al 2021). Indeed, since the nuclear rates are higher, a lower density is needed to reach the required amount of nuclear energy to counteract the contraction post He-b.…”

“…Arnett & Truran 1969;Lamb et al 1976;Weaver et al 1978;Sparks & Endal 1980;Arnett & Thielemann 1985) but, interestingly, it still remains a topic of lively research today. For instance, Gasques et al (2007), Pignatari et al (2013) discussed the impact of the 12 C + 12 C rates on the s-process occurring in C-burning regions; Sukhbold & Adams (2020) studied the impact of the core C-burning phase on the final fate of red supergiants; Fields et al (2018), in a very exhaustive study of the impact of nuclear uncertainties in models for pre-supernovae, identified, among the reactions having the largest impact on the pre-supernova structure, the reaction 12 C( 12 C,p) 23 Na; Chieffi et al (2021) have investigated the impact of new rates for the carbon fusion reaction in stellar models.…”

“…We also use simpler models, where we focus on the detailed abundances variations resulting from a very large nuclear reaction network (following more than 1400 isotopes). Compared to the recent work by Chieffi et al (2021), here we use different experimental data for the nuclear reaction rates that, as we shall see, lead to very different consequences.…”